FAA spokesman Bill Shumann said the restrictions will be greater than normal, following the raising of the terrorist threat-alert level in the United States.

"They will go beyond the normal ban on air travel within a three nautical-mile radius.. and up to 3,000 feet above ground," Shumann said.

In addition, the FAA said the following restrictions went into effect at 10 a.m. EDT Wednesday:

• Suspension of all waivers of temporary flight restrictions over sporting events. This includes companies that had been given waivers to fly blimps and banner-towing planes over sports arenas.

• Suspension of certain waivers for the existing flight-restricted zone of 15 nautical miles around the Washington Monument in the nation's capital. Crop dusters and aerial photographers are two of the groups which will not be allowed to get waivers. News helicopters will still be able to fly.

• Reinstatement of the gateway airport in the Washington area. General aviation aircraft flying into or out of three airfields in the DC area -- Potomac Airfield, Hyde Field and College Park Airport -- will be required to stop at Tipton Airfield in Tipton, Maryland, to be screened by the Transportation Security Administration (TSA).

Additional security measures are also being taken at the nation's airports, according to the TSA.

TSA spokesman Brian Turmail said security enhancements would vary airport by airport, according to a "tiered approach" plan developed by the agency.

The additional security measures could include these efforts.

• Additional screening of some passengers at the gate or security checkpoint.

• More police and canine patrols at the airport.

• Additional inspection of cars and restriction of parking.

• More signs and announcements to the public to be alert for suspicious activity or bags.